Photolithography is one of the important steps in the semiconductor manufacturing technology, which is able to transfer patterns in a reticle to a wafer (or substrate). Thus, a photolithography process is considered as a key step in the manufacturing of Very-Large-Scale-Integrations (VLSIs). The series of complex and time-consuming photolithography processes in the semiconductor manufacturing are mainly achieved by a corresponding exposure apparatus. The development of the photolithography technique, or the progress of the exposure apparatus are mainly focused on three major factors, critical dimension, overlay accuracy, and production capacity.
During the manufacturing of semiconductor structures, an exposure process includes three major steps: changing wafer on a wafer stage; aligning the wafer on the wafer stage with a reticle; and exposing to transfer the patterns on the reticle to the wafer. The step of aligning the wafer with the reticle includes detecting the levelness; and detecting the alignment marks. Detecting the levelness refers to detecting the levelness of the wafer; and detecting the alignment marks refers to detecting the alinement marks formed on the wafer. By detecting the levelness and the alignment marks, the position relationship of the wafer stage, the wafer and the reticle can be formed.
The detection of the wafer levelness is often performed before the alignment mark detection and the exposure of photoresist. The methods for detecting the levelness of the wafer are usually non-contact methods. The commonly used non-contact methods include optical methods, capacitive methods, and pressure methods, etc.
In the existing scan-projecting exposure apparatus, optical methods are often used to detect the levelness of a wafer (or substrate). The levelness detection is realized by a levelness detection unit of the exposure apparatus. The levelness detection unit includes a light-emitting unit and a light-receiving unit. The light-emitting unit is used to emit a levelness-detecting light; and the light-receiving unit is used to receive the levelness-detecting light reflected by the substrate.
FIG. 1 illustrates an existing method for detecting the levelness of a wafer. The method includes providing a semiconductor substrate 100; and forming a dielectric layer 101 on the semiconductor substrate 100. The method also includes forming a filling layer 102 on the dielectric layer 101; and forming a photoresist layer 103 on the filling layer 102.
Then, the semiconductor substrate 100 is loaded on the wafer stage of an exposure apparatus to perform the levelness detection before an exposure process. The light-emitting unit 11 of the levelness detection unit (not labeled) emits a levelness-detecting light. The levelness-detecting light irradiates the semiconductor substrate 100; and is reflected by the semiconductor substrate 100. At the same time, the light-receiving unit 12 of the levelness detecting unit receives the levelness-detecting light reflected by the semiconductor substrate 100. During the levelness-detecting process, the levelness-detecting unit scans along the scanning direction 13 parallel to the surface of the semiconductor substrate 100.
However, the accuracy of such a levelness-detecting method is limited by certain factors. The disclosed device structures and methods are directed to solve one or more problems set forth above and other problems.